U.S. Pat. No. 3,894,031, issued July 8, 1975, discloses, inter alia, that compounds having the formula ##STR3## wherein R' and R" are the same or different and can be hydrogen, alkyl, haloalkyl, cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, or heterocyclic, or the group --NR'R" can be a heterocyclic group, are useful for the treatment of hypertension.
U.S. Pat. No. 3,971,823, issued on July 23, 1976, discloses that compounds having the structure ##STR4## wherein R.sub.1 is alkyl or arylalkyl, are useful for the treatment of hypertension.